What Hormones Rise During Pregnancy Key Changes?

Pregnancy is driven by a remarkable hormonal shift. From the moment an embryo implants, the body begins producing rising levels of human chorionic gonadotropin (hCG), progesterone, and estrogen, followed later by hormones like human placental lactogen and relaxin. These changes support the growing fetus and reshape nearly every system in the mother’s body.

The most dramatic early change is the surge of hCG, which signals the body to sustain the pregnancy and is the hormone most pregnancy tests detect. Progesterone rises steadily to maintain the uterine lining and relax smooth muscle, while estrogen climbs throughout pregnancy to support blood flow and fetal development. Each hormone has a distinct role, and understanding them explains many of the physical changes women experience along the way.

What Hormones Rise During Pregnancy Key Changes?

The main hormones that rise during pregnancy are human chorionic gonadotropin, progesterone, estrogen, human placental lactogen, and relaxin. Each one follows its own timeline and produces specific effects on the body.

These hormones come from two main sources. Early on, the corpus luteum — a temporary structure in the ovary — produces progesterone and estrogen. Around the end of the first trimester, the placenta takes over as the primary hormone factory and produces increasing amounts of all these hormones for the rest of the pregnancy.

A point that often surprises people: the placenta is not just a passive filter. It is an active endocrine organ that produces hormones essential to pregnancy. This is why the hormonal changes of pregnancy are so widespread and sustained.

What Does hCG Do in Early Pregnancy?

Human chorionic gonadotropin is the first hormone to rise sharply after implantation. It is produced by the developing placenta and its primary job is to signal the corpus luteum to keep making progesterone.

Without hCG, the corpus luteum would break down, progesterone would fall, and the pregnancy would not be maintained. hCG levels rise rapidly in early pregnancy, roughly doubling every two to three days during the first weeks, though the exact pattern varies between individuals. Levels typically peak around the end of the first trimester and then decline to a lower plateau for the remainder of pregnancy.

hCG is the hormone that home pregnancy tests detect in urine. Its rapid rise is also the reason some women experience nausea in early pregnancy, since hCG peaks around the same time morning sickness tends to be most intense. That link is well supported, though the full cause of pregnancy nausea involves other factors as well.

Why Does Progesterone Rise So Much?

Progesterone rises steadily throughout pregnancy and reaches very high levels by the third trimester. Its main roles are to maintain the uterine lining, prevent uterine contractions that could cause early labor, and support the placenta.

Progesterone also relaxes smooth muscle throughout the body. This single property explains a wide range of pregnancy symptoms:

• Relaxed muscles in the digestive tract slow digestion and can cause constipation and heartburn
• Relaxed blood vessel walls contribute to lower blood pressure and dizziness
• Relaxation of the gallbladder and urinary tract can increase the risk of gallstones and urinary infections

Progesterone also plays a role in preparing the breasts for milk production and helps regulate the immune response so the mother’s body does not reject the fetus. Its effects are so broad that many pregnancy discomforts trace back to this one hormone.

What Does Rising Estrogen Do During Pregnancy?

Estrogen climbs throughout pregnancy and reaches its highest levels in the third trimester. It supports the growth of the uterus, increases blood flow to the placenta, and helps prepare the breasts for breastfeeding.

Estrogen also affects other systems. It contributes to increased blood volume, which is necessary to supply the growing fetus but can cause swelling and a feeling of breathlessness. It influences the development of the fetus’s organs and plays a part in triggering labor later on.

One important clarification: estrogen does not act alone. Its effects during pregnancy are shaped by the presence of high progesterone and other hormones. The balance between them matters as much as the level of any single hormone.

What Is Human Placental Lactogen and What Does It Do?

Human placental lactogen, also called human chorionic somatomammotropin, is produced by the placenta and rises throughout pregnancy. Its main role is to adjust the mother’s metabolism to support fetal growth.

This hormone reduces the mother’s sensitivity to insulin, which means her cells take up glucose less readily. That change helps ensure a steady supply of glucose for the fetus, which uses it as a primary energy source. The trade-off is that it raises blood sugar levels in the mother, which is why pregnancy can unmask or worsen glucose intolerance.

Human placental lactogen also promotes the breakdown of fats for energy and supports breast development. In pregnancies where this hormone is low, fetal growth can be affected, though the relationship is complex and not fully understood.

How Does Relaxin Change the Body?

Relaxin is produced by the corpus luteum early in pregnancy and later by the placenta and uterine lining. It rises to a peak in the first trimester and then stays elevated, with levels highest in early pregnancy.

Relaxin’s best-known effect is loosening the ligaments and connective tissue in the pelvis to prepare for childbirth. This helps the pelvis widen but can also cause joint instability and lower back or pelvic pain. Relaxin also relaxes blood vessels, contributing to the drop in blood pressure many women notice in early pregnancy.

The evidence on relaxin’s exact role in human pregnancy is more limited than for some other hormones. Some of what is known comes from animal studies, and the full picture in humans is still being studied.

How Do These Hormones Change Across Trimesters?

The pattern of hormone rise differs by trimester. hCG peaks early and then declines, while progesterone, estrogen, and human placental lactogen climb steadily and reach their highest levels near the end of pregnancy.

Here is a general overview of the timing and main source of each hormone:

The exact levels vary widely between individuals and even between pregnancies in the same person. This is why clinicians rely on patterns and ranges rather than a single number.

What Other Hormones Change During Pregnancy?

Several other hormones shift during pregnancy, though less dramatically than the main five. Oxytocin rises toward the end of pregnancy and plays a central role in labor and breastfeeding. Prolactin increases to prepare the breasts for milk production.

Thyroid hormones also change. The thyroid gland typically produces more thyroid hormone during pregnancy to meet increased metabolic demands, and iodine needs rise. Because thyroid problems can affect both mother and baby, thyroid function is often checked during pregnancy.

Cortisol, the body’s main stress hormone, also rises. This is normal and helps mobilize energy, but very high or very low levels can signal a problem. The adrenal and pituitary glands adjust throughout pregnancy to keep the system balanced.